California’s annual rainy season is getting underway about 27 days later now than it did in the 1960s, according to new research. Instead of starting in November, the onset of the rains is now delayed until December, and the rain, when it comes, is being concentrated during January and February.

“The onset of the rainy season has been progressively delayed since the 1960s, and as a result the precipitation season has become shorter and sharper in California,” said Jelena Lukovic, the lead author of the study. Lukovic is a climate scientist at the University of Belgrade in Serbia.

Less rain is falling in the so-called shoulder seasons of autumn and spring, and more is falling during the core winter months.

The worst fires occur in the fall, rather than in the hottest summer months, because that’s when vegetation is at its maximum dryness.

In a state that just endured its worst wildfire season in history, this doesn’t come as good news. In California during 2020, about 4.3 million acres burned in nearly 10,000 fires, resulting in 33 fatalities, according to the California Department of Forestry and Fire Protection (Cal Fire).

Researchers found that summer-like weather conditions were extending into October and November. The fall and winter seasons are also the time when strong, desiccating offshore winds develop in California.

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